2.2 ESTIMATION OF FLUID FLUX AND HYDRAULIC CONDUCTIVITY
2.2.2 Hydraulic Conductivity Estimation
LITERATURE REVIEW
that at low river flows, reliable Darcy velocities of the riverbed were obtained using this method. However, they found this method had limitations under transient flow conditions.
Irvine et al. [2015b] evaluated the application of amplitude, phase and combined methods for the determination of water flux and thermal diffusivity. For this purpose, they measured vertical temperature profiles through experiments conducted in a sand column.
These measured time series data further utilized for fluid flux estimation using phase and amplitude methods using VFLUX 2 program routine which includes Hatch et al. [2006]
and Keery et.al [2007] analytical solutions. Their study suggested that amplitude and phase methods performed well during steady-state conditions however, the use of amplitude method provided better estimations of fluid flux during transient flow conditions.
In addition, Ren et al. [2018] characterized the dynamics of water flow and heat transport in riparian zones using heat as tracer through laboratory-based experiments conducted in a sand tank. They investigated the effect of hydraulic head (with two different heads - 25 cm and 45 cm), radiation temperatures (with no radiation and 22°C) and water temperature (with three different temperatures - 4°C, 6°C, and 9.5°C) on water flow and heat transport through experimental approaches as well as 2-D Hydrus Model. The results of the study showed that a good agreement of the predicted and observed thermal dynamics variation of the 2-D sand tank and also indicated that hydraulic head was the major mechanism for water flow and thermal dynamics variation. Also, the sensitivity analysis of this study results illustrated that the model was most sensitive to hydraulic head (H), followed by Van Genuchten parameter (α), permeability coefficient (Ks), water temperature (T), Van Genuchten parameter (n), residual moisture content (θr), and saturated moisture content (θs).
Over past few years, various research studies have been employed to estimate the riverbed hydraulic conductivity using different methods and techniques include field approaches such as use of seepage meter [Isiorho and Meyer, 1999]; in-situ permeameter [Rosenberry, 2000; Landon et al., 2001]; slug tests [Landon et al., 2001; Baxter et al., 2003], laboratory measurements, [Cai et al., 2015] numerical and analytical modelling techniques [Mutiti and Levy, 2010; Pozdniakov et al., 2016]. Table 2.1 shows some of the studies carried out for the estimation of riverbed hydraulic conductivity using different methodologies and techniques. In recent years, research interest has been increased on using environmental tracers such as heat for fluid flux estimations in hyporheic zone [Anderson, 2005; Duque et al., 2010; Engeler et al., 2011; Ravazzani et al., 2016].
Table 2.1: Few studies carried out for the estimation of riverbed hydraulic conductivity using different methodologies and techniques.
Researcher Year Work Method/Approach/Technique Major Observations or Findings
Chen 2000 Measurement of streambed hydraulic conductivity
Using L-shaped standpipes directly to streambeds
Hydraulic conductivities measurements in horizontal, vertical and also in oblique directions
Chen 2004
Measurement of streambed hydraulic conductivity for rivers in South Central Nebraska
Using extend permeameter
The anisotropy of channel
sediments can be determined from streambed tests of similar
sediment volumes
Cheng and Chen 2007
Evaluation of methods of determination of hydraulic properties in an aquifer-aquitard system
Using the inverse modelling approach with MODFLOW
The combination of permeameter and direct push technique is less expensive than pumping tests
Cheong et al. 2008 Estimation of hydraulic conductivity in a riverside alluvial system in South Korea
Using grain-size analysis, pumping and slug tests and numerical modelling
Hydraulic conductivities
estimated from pumping test and grain size analysis are found to higher than the estimations of slug test
Wojnar et al. 2013
Investigation of the ability of geophysical profiling techniques to determine hydraulic conductivity
Using seepage meter, slug test and heat- flow modelling
Geophysical methods cannot be used alone to assess appropriate vertical hydraulic conductivity ranges
Shamsuddin et al. 2019
Determination of vertical hydraulic conductivity at Muda River riverbank filtration site, Malaysia
Using rain size, pumping test and in situ falling head standpipe permeability tests.
Grain size data provided reliable estimates of hydraulic
conductivity than pumping and permeability tests
Using heat transport modelling is an accurate and cost-effective technique [Lautz, 2010] and recent studies focused on using heat as a tracer for the assessment of riverbed hydraulic conductivity [Woodbury and Smith, 1988; Bravo et al., 2002; Niswonger, 2003].
While Mutiti and Levy [2010] used heat flow model for investigating the variability of riverbed hydraulic conductivity during storm events along the Great Miami River in Southwest Ohio. In their study, the response of variation in hydraulic conductivity for the storm event’s rising limb was correlated.
However, the error in the estimation of fluid flux can propagate the error in streambed hydraulic conductivity estimations which can strongly influence the river- aquifer interaction process [Kalbus et al., 2009; Irvine et al., 2015; Tang et al., 2017].
Hence, it is necessary to understand the reliability of water flux estimations for heterogeneity streambed conditions using heat transport model in real field conditions. But, an assessment of the actual impacts of heterogeneity in a real field situation using heat transport models is somewhat difficult, and accurate representation of real heterogeneity in a model remains challenging and numerical instabilities may arise [Schornberg et al., 2010]. The heterogeneous streambed hydraulic conductivities can be determined using Darcy relations with the fluid fluxes in the soil. The fluid fluxes in the soil can be empirically related with temperature variations [Kalbus et al., 2009]. Hence using representative field soils in laboratory and measuring temperature variations using thermal sensors, fluid fluxes are first estimated. Thereafter, the streambed hydraulic conductivity is obtained by parameter estimation technique in the Darcy flow equation.